Conventional methods for producing a field emission source by using a nano-sized electron emission material (hereinafter, referred to as “nano-material”) in a particle or rod form can be divided into a method for growing a nano-material directly on a cathode substrate [(Science vol. 283, 512, 1999), (Chemical Physics Letters. 312, 461, 1999), (Chemical Physics Letters. 326, 175, 2000), (Nano Letter vol. 5, 2153, 2005), US006350488B1, US006514113B1], and a method for variously attaching a synthesized nano-material in a powder form onto a cathode substrate such as a suspension filtering method [(Science vol. 268, 845, 1995) and (Applied Physics Letters, vol. 73, 918, 1998], a screen printing method [(Applied Physics Letters vol. 75, 3129, 1999) and Korean Patent Application Publication No. 10-2007-0011808], electrophoresis [(Advanced Materials vol. 13, 1770, 2001), (Nano Letter vol. 6, 1569, 2006), US006616497 B1 and US20060055303A1], a self-assembling method [(Advanced Materials vol. 14, 8990, 2002) and US006969690B2], a spray method [(Mat. Res. Soc. Symp. Proc. vol. 593, 215, 2000), (Carbon vol. 44, 2689, 2006), (The Journal of Physical Chemistry C. 111, 4175, 2007), US006277318B1 and Korean Patent Application Publication No. 10-2007-0001769] and an inkjet printing method [(Small, vol. 2, 1021, 2006), (Carbon vol. 45, 27129, 2007) and US20050202578A1].
The directly growing method enables easy control of a structure of the nano-material such as control of a diameter, length, density and patterning, but is disadvantageous in that it is difficult to assure uniformity of catalyst metal deposition on a large area and control a size of catalyst metal particles, and adhesion between the grown nano-material and the cathode substrate is low. In order to overcome the problem in the adhesion between the nano-material and the cathode substrate, the difficulty in control of the physical properties and others as described above, methods for purifying, dispersing and functionalizing a nano-material in a powder form, which has been produced by various synthesis methods, so as to become a paste, and methods for attaching a suspension dispersed in a solvent and a surfactant onto various cathode substrates have been developed. Among those methods, the screen printing method, which fabricates a field electron structure by printing a paste composition containing nano-material powders, a polymer, a binder, an organic solvent, a metallic filler, other additives, etc., onto a cathode substrate and performing drying, exposing, sintering, surface-protrusion processes and others for the cathode substrate, provides superior adhesion between the cathode substrate and the field emission structure and is suitable for a large area. However, the screen printing method is disadvantageous in that it is difficult to control density of an active electron emission cite, the field electron emission characteristic is easily deteriorated due to various organic/inorganic binders and polymers, and processes are complicated.
The electrophoresis enables selective deposition at a room temperature and is easily applicable to a large area. However, since controlling thickness and density is difficult, uniformity and reproducibility are poor, and adhesion to the cathode substrate is low, there is a problem in reliability and stability when the electrophoresis is applied to field electron emission.
The self-assembling method has simple processes and is easily applicable to a large area at a room temperature. However, like the electrophoresis, the self-assembling method is disadvantageous in that the adhesion between the formed nano-material thin film and the cathode substrate is poor, and much time is needed.
The spray method also has simple processes and is easily applicable to a large area at a room temperature. However, since the thin film surface state is determined depending on a degree of evaporation of a suspension during movement of a spray droplet from a nozzle to the cathode substrate, control of thickness and density of a nano-material thin film and uniform deposition of a thin film are difficult. Accordingly, uniformity and reproducibility are deteriorated. Due to the low adhesion to the cathode substrate, detachment easily occurs during the field electron emission.
The inkjet printing method enables easy control of thickness and density, can realize selective patterning, and is suitable for a large area at a room temperature. However, the inkjet printing method is disadvantageous in that the adhesion between the printed nano-material and the cathode substrate is low.